This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application FLAT MASK AND METHOD FOR ASSEMBLING THEREOF, AND TENSION MASK ASSEMBLY MADE IN ACCORDANCE WITH THIS METHOD filed with the Korean Industrial Property Office on May 8, 2001 and there duly assigned Ser. No.0024972/2001.
1. Technical Field
The present invention relates to a flat mask for a cathode ray tube, an assembling method for assembling the flat mask, and a tension mask assembly manufactured by using the method.
2. Related Art
In general, a color cathode ray tube (CRT) for television and computer displays is a device for displaying images by guiding electrons emitted from an electron gun to strike and illuminate particular phosphor areas on an inner surface of the cathode ray tube. The cathode ray tube employs three electron beams, one for each of the primary color components (red, blue and green) of the color video signal, and employs a screen made up of an array of phosphor elements in the three primary colors. A shadow mask is interposed between the electron gun and the screen to permit each electron beam to strike only phosphor elements associated with the particular electron beam.
The shadow mask is usually contoured to be somewhat parallel to the inner surface of the cathode ray tube faceplate, and to be bowed outwardly for a path of the electron beams deflected by a deflection yoke.
Some electrons do not pass through the apertures of the shadow mask. Instead of passing through the apertures, these electrons hit the shadow mask, thereby heating the shadow mask locally. This localized heating causes a transient localized expansion of the mask known as xe2x80x9cdoming phenomenonxe2x80x9d. This doming can cause mislanding of the electron beams, which degrades the color purity of the display.
Therefore, shadow masks that are fixed on their frame with a predetermined tension, called a tension mask, have been developed to overcome the above-noted drawbacks and to meet the current trend of making displays large and flat.
Exemplars of efforts in the art include U.S. Pat. No. 4,942,332 for TIED SLIT MASK FOR COLOR CATHODE RAY TUBES issued to Adler et al. on Jul. 17, 1990, U.S. Pat. No. 3,638,063 for GRID STRUCTURE FOR COLOR PICTURE TUBES issued to Tachikawa et al. on Jan. 25, 1972, and Japanese Patent. No. P2000-133161 for COLOR CATHODERAY TUBE with publication date May 17, 2000 and listing inventors Minami Go, Kashihara Shiro, and Oshima Shigenari.
Tachikawa ""063 describes a tension mask using an aperture grill. In Tachikawa ""063, a plurality of parallel strips is stretched on a pair of opposed supporting members of a mask frame under predetermined tension. In this structure, when the shadow mask is heated by irradiation of electron beams during operation of the color cathode ray tube, the restoring force of the prestressed frame compensates elongation of the strips due to thermal expansion of that portion. Therefore, it is possible to avoid doming. However, in Tachikawa ""063, the strips of the tension mask are fabricated from a thin steel of about 0.1 millimeters (mm) in thickness and are stretched between a pair of supports without being connected to each other, and therefore they vibrate independently due to even a slight impact, which causes the tension mask to resonate. This phenomenon is referred to as howling.
Adler ""332 describes a slot-type tension mask to prevent the above-described problems. The slot-type tension mask for a color cathode ray tube comprises a series of parallel strips being disposed at a predetermined pitch and pattern, the strips being loosely coupled by widely spaced real bridges under tension. The strips are connected by real bridges, which are arranged so that the slots form a brick wall-like pattern. In addition, all strips terminate at the top and bottom in end members, which are welded to supporting members of the mask frame. Many slots are formed to pass electron beams emitted from an electron gun. In the tension mask of Adler ""332, the strips are connected by real bridges, thereby reducing howling somewhat. However, since the strength of the supporting ends located at edges of the tension mask is greater than that of the apertured portion, the stress is concentrated on the supporting ends so that the portions near the edges of the apertured portion are liable to vibrate.
The Japanese Patent No. P2000-133161 describes a tension mask to solve the above-described problems. In this structure, the tension mask comprises an apertured portion with a plurality of small slots and supporting ends located at edges of the apertured portion, which are fixed on the supporting members of the mask frame with a predetermined tension. A width of short supporting ends becomes wider from a center portion to each corner portion. Before applying tension to the flat mask, if the width of the center portion and the corner portion thereof are assumed to be xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d, respectively, the values are satisfied by the inequality 2xe2x89xa6b/axe2x89xa66. With regard to the flat mask, one side of the short supporting ends is half-etched and then the stress concentrated thereon is decreased, thereby increasing the tension acting on portions near the edges of the apertured portion when tension is applied. As to a tension mask assembly manufactured from the flat mask, the tension acting on portions near the edges of the apertured portion can be the same as that of the central apertured portion by making the width of the each corner portion of the short supporting ends greater than that of central portion thereof by a predetermined ratio, and by half-etching one side of the short supporting ends.
In the Japanese Patent No. P2000-133161, there is a limitation that the width of the corner portions of the short supporting ends should be twice more than that of the central portion thereof to prevent tension acting on portions near the edges of the apertured portion from being less than that of the central apertured portion. In addition, according to Japanese Patent No. P2000-133161, before applying tension, the apertured portion of the mask is formed to have a rectangular shape. As a result, since the mask is expanded longitudinally while being compressed transversely when the shadow mask is applied under tension, slots at portions near the edges of the apertured portion are displaced.
Therefore, the Japanese Patent No. P2000-133161 does not solve all problems, because apertured portions of the tension mask do not maintain a rectangular shape. In addition, since one side of the short supporting ends is half-etched, the mask is liable to bend toward half-etched portions after being held under tension.
While these recent efforts provide advantages, I note that they fail to adequately provide an efficiently and conveniently improved flat mask for cathode ray tube, and assembling method thereof.
It is therefore an object of the present invention to provide a flat mask of which an apertured portion has satisfactory thermal expansion, uniform stress distribution and linearity, and the width of curved short supporting ends is formed to be the same in the longitudinal direction. The present invention also provides the flat mask, which is manufactured to prevent deformation caused by heat treatment after being held under tension.
Another object of this invention is to provide a method of assembling the flat mask with a mask frame, and a tension mask assembly assembled by using the above method.
In accomplishing these and other objects, according to a first aspect of the present invention, there is provided a flat mask comprising an apertured portion including a plurality of slots formed for passing electron beams and being separated at a predetermined interval, and a plurality of pin-cushion type or barrel type strips. The flat mask also comprises supporting ends including short supporting ends and long supporting ends facing edges of the apertured portion.
The width of the short supporting ends is formed to be the same in a longitudinal direction, and the short supporting ends are curved to have the same curvature as lateral edges of the apertured portion.
The width of the short supporting ends is w1, a half width of the apertured portion is w4, a distance between an end point of an inner boundary of the short supporting ends and a tangent line contacting a central point thereof is w3, an inequality 0.02w4xe2x89xa6w1xe2x89xa60.05w4 between the apertured portion and the short supporting ends, and an inequality 0 mm less than xc2x1w3xe2x89xa63.0 mm are satisfied. The w3 is represented as xe2x80x9c+w3xe2x80x9d in the concave pin-cushion type for FIG. 3 and xe2x80x9cxe2x88x92w3xe2x80x9d in the convex barrel type for FIG. 4.
In the apertured portion of the flat mask, it is preferable that the strips are connected by a plurality of real bridges forming the slots. In addition, the slots preferably include dummy bridges. A ratio of a longitudinal pitch Pv to a transverse pitch Ph of the real bridge preferably satisfies an inequality 5.0xe2x89xa6Pv/Phxe2x89xa612.0. The apertured portion and the supporting ends of the flat mask are preferably made of iron (Fe).
It is desirable that the longitudinal pitch of the real bridge Pv satisfies the inequality 2.0 mmxe2x89xa6Pvxe2x89xa610.0 mm, and removed volumes of the short supporting ends are preferably equal to or larger than removed volumes of the apertured portion by half etching the front and the rear side of the short supporting ends.
In the flat mask, a sloping side is preferably formed near the corner of the supporting ends and a tilt angle xcex8 of the sloping side relative to the longitudinal direction of the short supporting ends satisfies the inequality 0xc2x0 less than xcex8 less than 60xc2x0.
According to a second aspect of the present invention, there is provided a plurality of grooves 16 on a front and a rear side of the short supporting ends formed by half-etching. In addition, it is preferable that the grooves 16 are formed along the longitudinal direction, having the same curvature as the short supporting ends 14b. 
In addition, it is desirable that the grooves 16 are formed at the same transverse pitch as a transverse pitch of the slots formed in the apertured portion, and that the transverse pitch of the grooves 16 is less than 10% of the width of the short supporting ends when the width of the short supporting ends is less than 10 mm. The depth of the grooves is preferably 30-70% of a thickness of the supporting ends, and that the width of the grooves is 30-70% of the transverse pitch of the grooves.
Preferably, positions of the grooves on the front sides of the short supporting ends are different from those on the rear sides of them. Alternately, the grooves on the front sides of the short supporting ends can be opposite to those on the rear sides of them.
An assembling method of the flat mask comprises the steps of longitudinally applying tension to the flat mask in which the tension applied to portions near the edges of the flat mask is greater than the tension applied to a central portion of the flat mask, attaching the long supporting ends of the flat mask to supporting members of a mask frame by welding, and cutting off protruding portions extending from the mask frame of the long supporting ends.
A tension mask assembly is preferably manufactured by using the assembling method of the flat mask.
To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a mask, comprising: an apertured portion having curved sides and having a plurality of slots and strips, the slots being separated from each other by a predetermined interval, said apertured portion having a shape selected from among a pin-cushion shape and a barrel shape, the strips being shaped to form a pattern corresponding to the shape of said apertured portion, electron beams passing through the slots; and a plurality of supporting ends including two short supporting ends and two long supporting ends, the short supporting ends and the long supporting ends being located at respective edges of said apertured portion, the short supporting ends including a first short supporting end having an inner boundary located at one of the curved sides of said apertured portion and having an outer edge spaced apart from said apertured portion, the inner boundary being curved and extending from a first end point through a center point and to second end point, the first short supporting end having a width extending in a transverse direction from the inner boundary to the outer edge, the short supporting ends being curved to have substantially the same curvature as the curved sides of said apertured portion, said apertured portion having a width extending in the transverse direction; the width of the first short supporting end being w1 as measured from the center point of the inner boundary to the outer edge, half the width of said apertured portion being w4 as measured from center of said apertured portion to the center point of the inner boundary of the first short supporting end, the distance between the first end point and a tangent line extending from the center point of the inner boundary being w3 as measured in the transverse direction; the width w1 being less than or equal to 0.05w4, the width w1 being greater than or equal to 0.02w4, the absolute value of the distance w3 being greater than 0 millimeters, the absolute value of the distance w3 being less than 3.0 millimeters.
To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a flat mask for a cathode ray tube, comprising: a central part having curved sides and having a plurality of slots and strips, the slots being separated from each other by a predetermined interval, the strips being shaped to form a pattern corresponding to the shape of said central part, electron beams passing through the slots; and a plurality of supporting ends including two short supporting ends and two long supporting ends, the short supporting ends and the long supporting ends being located at respective edges of said central part, the short supporting ends including a first short supporting end having an inner boundary located at one of the curved sides of said central part and having an outer edge spaced apart from said central part, the inner boundary being curved and extending from a first end point through a center point and to second end point, the first short supporting end having a width extending in a transverse direction from the inner boundary to the outer edge, the short supporting ends being curved to have substantially the same curvature as the curved sides of said central part, said central part having a width extending in the transverse direction; the width of the first short supporting end being w1 as measured from the center point of the inner boundary to the outer edge, half the width of said central part being w4 as measured from center of said central part to the center point of the inner boundary of the first short supporting end, the distance between the first end point and a tangent line extending from the center point of the inner boundary being w3 as measured in the transverse direction; the width w1 being less than 0.05w4 and greater than 0.02w4, the absolute value of the distance w3 being greater than 0 millimeters and less than 3.0 millimeters.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. Other advantages and features will become apparent from the following description and from the claims.